PROJECT SUMMARY Inborn errors of metabolism (IEMs) are genetic diseases that cause illness and death in children; however, early detection and intervention permit children with some IEMs to develop normally. Lipoic acid deficiencies are a new class of IEMs that cause metabolic acidosis, seizures and severe neurodevelopmental abnormalities. Lipoic acid (LA) must be synthesized de novo in mammals and is an essential cofactor for fundamental enzymes in central carbon metabolism. Our lack of understanding LA metabolism and its relationship to metabolic programs is the primary obstacle in treating LA deficient patients. We have unique access to patient samples and through metabolomics analysis we have discovered a number of unexpected metabolic abnormalities associated with LA deficiencies; including elevation of 2- hydroxyglutarate (2-HG), a metabolite with wide reaching impacts on cell signaling and epigenetic regulation. We intend to characterize the LA metabolic pathway in human cells and identify mechanisms contributing to the elevation of 2-HG and its pathogenic role in LA deficiencies. We have multiple mouse models of LA deficiency including a novel knock-in model of a patient mutation that are embryonically lethal and with these models, we intend to investigate the impact of LA deficiencies on embryonic development. The central hypothesis of this proposal is that in mammals, impaired activity of mitochondrial enzymes due to LA deficiencies causes aberrant metabolism including accumulation of 2-HG, which contributes to abnormal development. If successful, this proposal will generate a definitive assessment of the role of distinct enzymes in the LA pathway on central metabolic fluxes in human cells, thereby providing a detailed view of the metabolic consequences of each LA-related human IEMs. It will also characterize the effects of dysfunctional LA metabolism in vivo during embryogenesis. The focus on patient-derived cells and mouse models should increase the disease relevance of the work covered in the proposal.